"""
617. Merge Two Binary Trees (Easy)
给定两个二叉树，想象当你将它们中的一个覆盖到另一个上时，两个二叉树的一些节点便会重叠。

你需要将他们合并为一个新的二叉树。合并的规则是如果两个节点重叠，那么将他们的值相加作为节点合并后的新值，否则不为 NULL 的节点将直接作为新二叉树的节点。

示例 1:

输入:
	Tree 1                     Tree 2
          1                         2
         / \                       / \
        3   2                     1   3
       /                           \   \
      5                             4   7
输出:
合并后的树:
	     3
	    / \
	   4   5
	  / \   \
	 5   4   7


"""


# Definition for a binary tree node.
class TreeNode:
    def __init__(self, x):
        self.val = x
        self.left = None
        self.right = None
class Solution:
    def mergeTrees(self, t1: TreeNode, t2: TreeNode) -> TreeNode:
        if t1 is None and t2 is None:return None
        if t1 is None:return t2
        if t2 is None:return t1
        root = TreeNode(t1.val+t2.val)
        root.left = self.mergeTrees(t1.left,t2.left)
        root.right = self.mergeTrees(t1.right,t2.right)
        return root


if __name__ == '__main__':
    root = TreeNode(3)
    root.left = TreeNode(9)
    root.right = TreeNode(20)
    root.right.right = TreeNode(7)
    root.right.left = TreeNode(15)

    print(Solution().mergeTrees(root))
